SILICON OXYCARBIDE COATINGS ON GRAPHITE FIBERS - CHEMISTRY, PROCESSING, AND OXIDATION RESISTANCE

Silicon oxycarbide coatings are applied to graphite fibers by dip coating tows of fibers into hexane solutions of the silsesquioxane terpolymer -[MeHSiO](0.1)[MeSi(OnPr)O](0.2)[MeSi(O)(1.5)](0.7) - to form silsesquioxane coatings typically 0.1 mu m thick. The coatings are then pretreated by heating in N-2 to selected temperatures in 200 degrees C increments to 1000 degrees C. The amorphous polymeric coatings were shown by (FTIR) analysis to convert to amorphous silicon oxycarbide coatings on heating to temperatures above 600 degrees C. The oxidation resistance of the pretreated coated fibers is compared with the oxidation resistance of uncoated fibers by heating tows of both types of fibers in static air for 3 h at selected temperatures to 800 degrees C, where the coated fibers barely survive heating for 1 h. The uncoated fibers do not survive heating in air at 700 degrees C even for only 1 h. Thus, the coatings increase fiber stabilities towards oxidation by 75-100 degrees C. All materials were characterized by FTIR analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and nuclear magnetic resonance where possible.